More evidence has emerged suggesting a link between pollutants found in oily fish and type two diabetes.
Pesticides found in oily fish could play a role in diabetes
An international team found high levels of persistent organic pesticides (POPs) in the blood correlated to insulin resistance, a precursor to diabetes.
POPs are stored in fatty tissues - the study suggested this may be why obese people are more vulnerable to diabetes.
However, experts have said that the study published in Diabetes Care is far from conclusive.
Patients resistant to the hormone insulin are unable to remove excess glucose from their blood, and this is normally an important step in the onset of type two diabetes.
The new research therefore suggests that POPs act critically at a very early stage in the development of diabetes.
In 2005 researchers in Sweden found people exposed to high levels of POPs were more at risk of developing type two diabetes.
They found higher levels of POP residues were present blood samples of men and women who had diabetes than in those who did not.
The authors of the current research, based at Kyungpook National University and the University of Minnesota, also previously found blood concentrations of POPs were linked to the prevalence of diabetes.
Obese patients with low POP levels had an unexpectedly low incidence of diabetes.
In the new study they observed a similar interaction between certain POPs and insulin resistance, even among non-diabetic patients.
No causal link
But the work does not confirm a causal link - it is possible that that having insulin resistance could reduce people's ability to clear POPs from their system, thus explaining the association.
Lead author Professor Duk-Hee Lee said the evidence needed to be replicated and developed in other studies, and called for molecular studies to explain the link between pesticides and insulin resistance.
Matt Hunt, Head of Science Information at Diabetes UK, said: "Insulin resistance is often observed as an early warning sign for developing diabetes and therefore possible contributors to this state are always of interest."
However, he said the current research was very complex and still speculative and did not provide a mechanism by the which the POPs could cause insulin resistance.
He said: "At the moment we would not conclude that the rise of obesity can be attributed to pesticide use, and should still be put down to increasingly unhealthy diets and lack of exercise."
Frankie Phillips, a dietician from the British Dietetic Association said: "This research is interesting but we need to have more details before we can say anything conclusive.
"It would be useful to avoid pesticides where possible, by washing fruit and vegetables, but it is still essential to reduce the burden of obesity to reduce the incidence of type two diabetes."
She added that there were clear benefits to eating oily fish, such as reducing the risk of heart disease, and recommended eating one portion a week.
Professor Lee agreed: "Even if POPs are causally related to diabetes, it is difficult for individuals to completely avoid POPs because they are detected in various foods.
"At present, the best thing we can do may be to avoid obesity, because obesity appears to increase the toxicity of POPs."